The specific aims of the proposal are related to two general areas. One area deals with the induction by radiation of Schwann cells, Schwann cell myelin and connective tissue constituents (hereafter referred to as intraspinal Schwann cell ISC) in spinal cords of immature rats. The aim of one study is to characterize in more detail the morphological relationships and interactions between the ISC and the normal cellular constituents of the spinal cord. A second study will evaluate the response of ISC to an indirect injury, by crushing the dorsal roots and subsequently following the patterns of degenerative and regenerative changes in the spinal cord and determining if the dorsal root axons are capable of regrowing into ISC-occupied areas of spinal cord. The third study is designed to determine the pattern of changes occurring in the ISC following the placement of a surgical wound into the spinal cord. A question basic to the latter two studies is whether ISC-occupied areas will respond in a manner characteristic of peripheral nerve or whether spinal cord cell reactions will predominate. These studies will utilize light microscopy, 3H-thymidine autoradiography, immunohistochemistry and axonal tracing techniques with horseradish peroxidase. The second general area deals with fluoride resistant acid phosphatase (FRAP), an enzyme associated with synapses in the dorsal gray matter of the rat. The aim of one study is to correlate changes in FRAP following sciatic nerve injury with certain cellular reactions that occur in the FRAP-containing areas following the same injury. A second study will evaluate the effects of ionizing radiation on the development of FRAP since this enzyme develops during the early postnatal period. These changes will be determined by both qualitative and quantitative histochemistry. All studies are related to the long-term goals of the project, which are: (1) to evaluate radiation-induced changes in the immature nervous system, (2) to use ionizing radiation as a tool to study reparative and regenerative capacities of the immature nervous system, and (3) to study normal postnatal development of the spinal cord. The studies involving ISC are related to attempts by others to transplant constituents of the peripheral nervous system (either nerve or Schwann cells) into the spinal cord in an effort to facilitate regeneration of the central nervous system.